The production of noxious nitrogen oxides (NOx) by internal combustion engines which pollute the atmosphere are undesirable and in many cases are controlled by regulations established by governmental entities. One method for limiting or controlling the combustion temperature of the engine and thus reduce NOx emissions has been to recirculate a portion of the exhaust gas back to the engine air intake to lower the oxygen content in the intake air. This reduces the combustion temperature of the intake charge and in turn reduces the amount of NOx formation during combustion due to lower flame temperatures.
In order to recirculate exhaust gas through an exhaust gas recirculation (EGR) line connecting the exhaust manifold to the intake air supply line, exhaust manifold pressure is maintained higher than the intake manifold pressure. However, this causes gas exchange pressure losses referred to as Pumping Mean Effective Pressure (PMEP). Furthermore, for operational efficiency the amount of exhaust gas to be recirculated should be varied based on operational conditions and the need to reduce NOx emissions. Therefore, systems and methods are needed to increase the efficiency of EGR systems by reducing PMEP and provide effective and reliable determinations of EGR flow rates for EGR control. The present invention is directed toward meeting these needs, among others.